1. Field of the Invention
This invention relates to a tape loading device and more particularly to a device for wrapping a magnetic tape a given degree of angle around the circumferential surface of a rotary drum, for example, in a helical scanning type magnetic recording and reproducing apparatus using the magnetic tape as a recording medium.
2. Description of the Related Art
The helical scanning type magnetic recording and reproducing apparatus such as a video tape recorder (VTR) or a digital audio tape recorder (DAT) is provided with a tape loading device. When the apparatus is loaded with a tape cassette, the tape loading device pulls a magnetic tape out from the tape cassette and wraps the magnetic tape around the outer circumferential surface of a rotary drum to a given degree of angle. In the case of an 8-mm type apparatus, for example, the rotary drum is arranged to have a small diameter and, therefore, the wrapping angle of the magnetic tape around the rotary drum increases. The wrapping angle must be at a given constant value. To meet this requirement, the tape loading device is provided with rail slots for guiding, along the rotary drum, guide posts (or guide rollers) which are arranged to pull the magnetic tape out from the tape cassette and to keep the magnetic tape in the state of being wrapped a given degree of angle around the rotary drum. The tape loading device also includes a holding mechanism which is arranged to hold the guide posts at the ends of the rail slots.
In the case of a typical example of the conventional tape loading device, almost the whole of each of the rail slots is formed by a guide rail which is molded with a plastic material. The end part of the rail slot is formed on a drum base which is made of an aluminum die-cast material. The guide rails permit reduction in weight while the end parts permit accurate positioning of the guide posts. In other words, in the example of the conventional device, each of the guide-post guiding rail slots substantially consists of two parts, one being formed by the guide rail and the other by the drum base.
In the conventional device which is arranged in the above-stated manner, the rail slot has joint parts in the paths of the guide posts. Therefore, a stepped difference in level would appear in each of the paths if two parts of the rail slot are not accurately positioned. Even if the two parts of the rail slot are accurately positioned at the time of assembly work, deformation of the guide rail which is made of a plastic material or positional deviation of the screws used for fixing the guide rail would bring about some stepped level difference in the paths. If the stepped level difference is excessive, it would prevent the smooth movement of the guide posts and cause jumping or irregular movement of the guide posts. The irregular movement of the guide posts then causes fluctuations in the tape wrapping position (height, for example) of the magnetic tape relative to the rotary drum and might result in unstable recording and reproduction characteristics. Further, the above-stated behavior tends to damage the magnetic tape to cause noises such as a dropout in a reproduced image or the like.